An endoprosthesis or intraluminal prosthesis is a medical device used in the treatment of diseased bodily lumens. One type of endoprosthesis used in the repair and/or treatment of diseases in various body vessels is a stent. A stent is a generally longitudinal tubular device formed of biocompatible material which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract, esophageal tract, tracheal/bronchial tubes and bile duct, as well as in a variety of other applications in the body. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the lumen.
Stents generally include an open flexible configuration. This configuration allows the stent to be inserted through curved vessels. Furthermore, this configuration allows the stent to be configured in a radially compressed state for intraluminal catheter implantation. Once properly positioned adjacent the damaged vessel, the stent is radially expanded so as to support and reinforce the vessel. Radial expansion of the stent may be accomplished by inflation of a balloon attached to the catheter or the stent may be of the self-expanding variety which will radially expand once deployed. Tubular shaped structures, which have been used as intraluminal vascular stents, have included helically wound coils which may have undulations or zig-zags therein, slotted stents, ring stents, braided stents and open mesh wire stents. Super-elastic materials and metallic shape memory materials have also been used to form stents.
A stent may be delivered to a specific location within a body lumen by a delivery device. The delivery device includes a delivery tube on which a reconstrainment band is supported, typically in coaxial relation therewith. A tubular stent is supported on the reconstrainment band, typically in coaxial relation therewith. A tubular sheath covers the stent in coaxial relation therewith and with the delivery tube. The reconstrainment band is fixed to the delivery tube to prevent axial displacement of the reconstrainment band relative to the delivery tube. The reconstrainment band engages the stent to prevent axial displacement of the stent relative thereto. The retention of the stent by the reconstrainment band maintains the axial position of the stent relative to the reconstrainment band and delivery tube when the sheath is axially displaced relative to the delivery tube and reconstrainment band. Without the retention of the stent provided by the reconstrainment band, axial displacement of the sheath relative to the delivery tube may cause associated axial displacement of the stent as a result of frictional contact between the sheath and stent.
The retention of the stent by the reconstrainment band is beneficial during deployment of the stent by providing for the longitudinal position of the stent within the bodily lumen to be maintained during relative axial displacement of the sheath. The longitudinal position of the stent within the bodily lumen is typically significant. The maintenance of the longitudinal position of the stent relative to the delivery tube may be particularly difficult during reconstrainment. The sheath may be longitudinally retracted relative to the delivery tube such that a distal axial portion of the stent is exposed by the sheath and a proximal axial portion of the stent remains covered by the sheath. Reconstrainment refers to the forward axial displacement of the sheath relative to the delivery tube such that the axial distal portion of the stent which was uncovered by the longitudinal retraction of the sheath is recovered partially or completely by the sheath. The forward axial displacement of the sheath may cause forward longitudinal displacement of the stent relative to the delivery tube and, typically, the bodily lumen as a result of contact between the sheath and stent. Consequently, the stent may be carried by the sheath. Limiting or completely preventing such forward displacement of the stent relative to the delivery tube and bodily lumen is typically advantageous.
The partial or complete uncovering of the stent which results from the retraction of the sheath relative to the delivery tube typically results in the radial expansion of the stent in an outward direction away from the reconstrainment band. Subsequently, the delivery tube and reconstrainment band mounted thereon are retracted or longitudinally displaced in the distal direction relative to the stent for removal of the delivery tube and reconstrainment band from the stent. The radial expansion of the stent may be sufficiently limited such that the radial clearance between the interior surfaces of the stent is less than the maximum radial dimension of the fins. Consequently, the retraction or rearward longitudinal displacement of the reconstrainment band relative to the stent may result in catching of the stent by the fins. Catching of the stent by the fins may impede the removal of the reconstrainment band and the attached delivery tube from within the stent. Also, catching of the stent by the fins may cause the stent to be carried by the reconstrainment band.
Also, the reconstrainment of the stent and the initial loading thereof in the delivery device typically entails radially compressing the stent in the inward direction between the sheath and delivery tube. During the inward radial compression of the stent, it is possible for one or more of the fins to not be aligned with any of the voids in the stent into which the fins typically extend. A fin which is not aligned with any void in the stent will normally contact the interior surface of the stent as a result of the inward radial compression of the stent in the vicinity of the fin. Contact between the fin and stent may result in catching of the stent by the fin. Catching of the stent on one or more of the fins can impede the inward radial displacement of the stent toward the band and the associated inward radial compression of the stent. Consequently, the longitudinal displacement of the sheath in the distal or forward direction relative to the delivery tube which typically provides the compression of the stent is impeded. Impeding the longitudinal displacement of the sheath in the distal or forward direction relative to the delivery tube 14 interferes with the reconstrainment of the stent, and the initial loading thereof between the sheath and reconstrainment band in the delivery device.